New article number is already in use...

Error:

The new article number is already being used by an article.

Explanation:

When renumbering old article numbers to new article numbers, the new numbers must be free to use. Existing numbers cannot be used as new numbers. This error message occurs when renumbering to a new article number and the new number is already in use.

Solution:

Check which "new" numbers are already in use and adjust these article numbers to a number that is not yet in use.

Or renumber the old number to another article number that has not yet been used.

After this, you can import the file again.